The disclosure relates to abrasive coatings. More particularly, the disclosure relates to pre-formed abrasive coatings which may be applied to a substrate.
Gas turbine engines may have one or more nested spools of compressor sections and turbine sections co-rotating about an engine axis. An exemplary two-spool engine has: a low speed/pressure spool comprising a low speed/pressure compressor (LPC) and a low speed/pressure turbine (LPT); and a high speed/pressure spool comprising a high speed/pressure compressor (HPC) and a high speed/pressure turbine (HPT). The core flowpath of the engine passes air sequentially through the LPC and HPC to the combustor where it mixes with fuel and combusts. Combustion gases then proceed further downstream along the core flowpath through the HPT and LPT. Thus, the turbine sections may drive the rotation of their respective associated compressor sections. Optionally, one or more fan sections may be driven by the LPT or another turbine section. The fan sections drive air along a bypass flowpath, bypassing the core to produce additional thrust.
The individual compressor and turbine sections may be centrifugal or axial in configuration. In exemplary axial configurations, each section may have a number of stages. Each stage comprises an annular array or row (stage) of rotor blades. The blade stage may have an associated adjacent stage of stator vane airfoils. The airfoils are shaped to turn, accelerate and compress the working fluid flow in the compressor, and to generate lift for conversion to rotational energy in the turbine.
In a number of locations it may be desired to minimize clearance between relatively rotating components. A main example is the clearance between blade tips and the adjacent inner diameter (ID) surface of non-rotating structure. This ID surface is often formed by the ID surfaces of a circumferential array of blade outer air seal (BOAS) segments. The ID surface may be formed by an abradable ceramic coating on the ID surface of a metallic substrate of the BOAS segments. To interface with the abradable coating, the blade tips may bear an abrasive. The abrasive functions to abrade the abradable coating and provide a wear-in to a low radial clearance value between blade and BOAS. Low clearance means low blow-by of gas between tip and BOAS and thus high efficiency.
Many methods have been proposed for applying abrasive to blade tips. These include direct plating and direct spraying methods. Additionally, use of pre-formed abrasive has been proposed. U.S. Pat. No. 7,063,250 of Ohara et al., issued Jun. 20, 2006, discloses forming a squealer tip preform by plating an MCrAlY matrix and cubic boron nitride (CBN) abrasive to a brazing filler sheet. The preform is then brazed to the tip of a main airfoil substrate. U.S. Pat. No. 8,616,847 of Allen, issued Dec. 31, 2013, discloses forming a squealer tip preform by plating an MCrAlY matrix and cubic boron nitride (CBN) abrasive to a squealer tip preform. The preform is then brazed to the tip of a main airfoil substrate.